1. Field of the Invention
The present invention relates to programmable controllers used in industrial control applications such as those found to control material handling, metal cutting, packaging, assembly, batch sequencing, grinding, welding, polymer blending and handling, as well as energy management.
2. Description of the Prior Art
Since the advent of programmable controllers in the early 1970's (such as that disclosed in U.S. Pat. No. 3,686,639), these devices have been able to replace the hard wire relay logic control systems used in many industrial control applications. In the ensuing years, they have become more powerful, replacing not only relay ladder-type control programs, but also performing non-relay functions such as timing and counting, as well as performing data manipulation and transfer such as that disclosed in U.S. Pat. No. 3,930,233. Indeed, programmable controllers have become so powerful in recent years, controlling virtually thousands of outputs and performing many diverse and complicated data manipulation and transfer operations that they in many circumstances can replace the minicomputer for controlling complex industrial control systems. The Modicon 1084 Programmable Controller disclosed in pending U.S. patent applications Ser. No. 646,412 filed Jan. 2, 1976, now abandoned, and divisional application Ser. No. 873,407 filed Jan. 30, 1978, now U.S. Pat. No. 4,162,536 are characteristic of these large, high-powered controllers/data processors.
It has also been found during the relatively short history of the programmable controller that a need existed for small, low cost programmable controllers to replace control programs that would normally utilize eight or more hard-wired relays. It has further been found that it is at times desirable to allow the control engineer to program not only ladder-type control programs with each rung of the ladder representing an electrical circuit line having one or more nodes or contacts and a coil output which may be referenced to other nodes, but also a network of logic lines with interconnections between nodes of adjacent lines. Some companies such as Texas Instruments and Allen-Bradley have provided programmable controllers with programming panels capable of being programmed with control networks which can have interconnections between adjacent lines within the network. However, it has been found that, due to the type of solution employed by these programmable controllers, constraints had to be placed upon the user in terms of the number of vertical connections that could be placed between adjacent lines as well as the number of nodes that could be encompassed within two vertical lines of the control program. The present invention eliminates these problems in prior art programmable controllers by providing a control network without any limitations on the user in terms of the number of vertical interconnections that can be made within the network nor in the arrangement of nodes between vertical interconnections of the network. This is achieved by the utilization of what is called a "column solver" which for each network solves the vertical power flow in both the up and down directions for each node in a column.
The present invention also provides a programmable controller with improvements not found in prior art programmable controllers, such as the capability of inserting one or more networks between two existing networks so as to effectively re-number the remaining networks and thereby insure correct sequential solution of the networks where such a solution is desired.
The output point in the I/O system to which the coil output of a user line references, is assignable by the user and not dictated by line number. This further reduces the constraints placed on the user in formulating his or her control program.
The present invention also provides a programmable controller that has multiple discrete outputs on some calculate functions. These multiple outputs facilitate use of the result of the calculate function by the control engineer. Furthermore, the present invention not only provides for discrete input/output but also register input/output on the same I/O modules for the transferral of data to and from the programmable controller and interconnected devices such as other programmable controllers in a hierarchical control arrangement. In addition, the present invention provides a cursor display on its CRT which allows the user to have the real-time display of power status at any particular node in any selected line of the ladder-diagram network. Specialized search features are also present to the user.
In addition, the present programmable controller is housed in a unique modular arrangement suitable to a rugged industrial environment. The various features of the mechanical aspects of the present invention are disclosed and claimed in a co-pending patent application filed simultaneously with the present patent application; namely, U.S. patent application Ser. No. 883,277, filed May 3, 1978, U.S. Pat. No. 4,215,386.
All of the improvements synergistically combine to provide a low cost, flexible, and easily viable programmable controller.